If you are going to flag boost this achievement it helps tremendously to have the host create lag. Every flag caught will be worth more, sometimes MUCH more, if the host is lagging. Obiously don't do this unless everyone in the lobby is a booster so that nobody's game is disrupted.
You can tell who's host simply by looking at the second player down in the lobby. If he appears in the 2nd position for multiple players, he's the host.
It's easier to create significant lag via uploading as opposed to downloading. Go to gmail and upload a huge attachment (up to 25 MB), discard it and do it again. If that's not enough fire up hotmail and do the same thing, though the file size limit for hotmail is only 10 MB.
For easier results go to a photo site like Kodak Gallery or whatnot and upload a huge amount of digital pictures. The upload should run for a decent amount of time, hopefully for the duration of the match. Just do it again for the next match.
With the host creating lag the flag catchers will get 1000-2000 points per game. Only the host needs to create lag, though. Other players creating lag will have no effect.